Apparatus for electro-medical investigation

ABSTRACT

A medical diagnostic apparatus for producing an audible indication of the nature of electric signals produced in the human body by the action of the heart. An audio frequency carrier wave is modulated both in frequency and in amplitude in accordance with the aforesaid applied electric signals. The level of the fundamental tone normally remains below the limit of audibility. This limit is exceeded only when an electric heartbeat signal occurs.

United States Patent J anssen [451 Mar. 21, 1972 [54] APPARATUS FORELECTRO-MEDICAL 3,338,234 8/1967 Kleinerman et aL. ...128/2.06 RINVESTIGATION 3,426,150 2/ 1969 Tygart ...l28l2.06 R 3,413,546 11/1968Riehl et a1. ..l28/2.06 R [72] Inventor: Frits Jacques Janssen,Emmasingel, Eindhoven, Netherlands FOREIGN PATENTS OR APPLICATIONS 73Assignee; Philips Corporation, New York, NY 250,557 11/1966 Austria128/206 R [22] Filed: 2, 1969 Primary Examiner-William E. Kamm 21 Appl.No.: 881,462 Tnfa" [30] Foreign Application Priority Data [57] ABSTRACTDec. 4, 1968 Netherlands ..6817326 I A medical diagnostic apparatus forproducing an audible indication of the nature of electric signalsproduced in the human [52] U.S. Cl. ..128/2.06 A y y h ion f h heart- Anaudio frequency carrier [51 1111.01. ..A61l5/04 wave is modulated bothin qu n y a d in mplitude in ac- 53 Field 01 Search 1 28/206 A, 2.06 F,2.06 R, eerdenee with the aforesaid pp electric eignele- The level 123/21 A, 2 5 T of the fundamental tone normally remains below the limit ofaudibility. This limit is exceeded only when an electric heart-References Cited j fw fifi fi occurs W A UNITED STATES PATENTS 2,918,05412 1959 Qoolltasian ....128/205 T 4 Claims 2 Drawing 4 SJ 9 10 11 5 FMAM MOD PATENTEDMAR21 I972 -55 AMP AMP 6 FM MOD) AM MOD AF osc 7\J;

T flgJ INVENTOR. FRITS JACQUES JANSSEN BY (K M /K v ENT APPARATUS FORELECTRO-MEDICAL INVESTIGATION This invention relates to an apparatus forproviding an audible indication of the strength of electro-physiologicalsignals produced in the human body, for example, electrical voltages andcurrents produced by the action of the heart. Such apparatus are knownin which an audiofrequency carrier wave is used whose frequency ismodulated by the applied signals, while signal strength alterationsbecome manifest by variations of the pitch of the tone. In this mannerdeviations from the normal course of given physiological phenomena maybe assessed before other apparatus particularly designed for such anexamination is available, particularly in emergency cases, when a quickassessment of deviations may be decisive of the manner of treatment of apatient, useful indications can be obtained. It has been found that thesize and the weight of apparatus of this kind, which are energized bybatteries, may be readily restricted to such an extent that they can beadded without any objection to the portable instruments required for amedical examination.

Like the electrocardiograph such an apparatus can pick up the electricalsignals from the heart, which are then reproduced in the form of a soundvarying in pitch. The constantly audible fundamental tone makes thedistinction of the separate heart complexes difficult so thatauscultation is a fatiguing strain.

There has been employed a suppressed carrier wave which provides at eachpulse an audible tone as a result of the electrocardiogram signals, saidtone having a given frequency and a very short duration. The sound inthe pulse intervals is thus reduced to a level below the limit ofaudibility, but the perceptible sound does not contain information aboutthe signal strength.

The invention has for its object to avoid said disadvantages and tofacilitate quick recognition of the most lethal cardiac diseases such asfibrillation, arrest and arrhythmia. According v to the invention theaudiofrequency carrier wave is modulated in accordance with the appliedelectrical signal both in frequency and in amplitude. The amplitudemodulation may be adjusted so that the sound level of the nonaudibleaudiofrequency tone is raised in the presence of a signal until thelimit of audibility is transgressed, after which alterations of thesignals become manifest in differences of pitch and strength. In thiscase the sound level of the fundamental tone may be reduced to a valuebelow the limit of audibility without the desired information gettinglost or being markedly weakened.

The invention will be described in greater detail by means of thefollowing description of a preferred embodiment thereof in conjunctionwith the accompanying drawing, in which:

FIG. 1. is a simplified circuit diagram of the apparatus in accordancewith the invention, and

FIG. 2. relates to one embodiment of the apparatus.

By means of the input electrodes 1, 2 and 3, electrical signals producedby the heart beat in the human body are derived and applied to a simpleelectrocardiogram amplifier 4, in which the derived signals are combinedin known manner into a single signal voltage. This signal voltage isapplied to an audiofrequency oscillator 5, the frequency of which ismodulated by the signal voltage so that, e.g., an increase in signalvoltage may result in a rise of frequency and hence the pitch of thefundamental tone is raised. By means of the switch 6 the DC currentsource 7, preferably formed by dry cell batteries or a different easilymanipulated current source of small size, is put in or out of operation.The signal supplied by the amplifier 4 is applied via the rectifier 8 tothe amplitude modulator 9 which modulates the amplitude of thefrequency-modulated signal coming out of the audiofrequency oscillator 5in accordance with the strength of the signal from the amplifier 4. Anamplifier 10 with gain control supplies the signal to the soundreproducing device 11 in which it is converted into an audible tone.

The required parts of the circuit described are accommodated in ahousing 12 composed of a suitable synthetic resin. The shape of thehousing [8 to some extent adapted to the manner in which the apparatusis employed. For establishing the electric connection between the inputelectrodes 1, 2 and 3 and the body surface, that is to say, the patientsthorax in the case of an examination of the heart, the required numberof contact arms 13, 14 and 15 are provided on the housing 12. These armsmay, if necessary, be movably fastened in order to allow some relativedisplacement. The housing is furthermore provided with a rocker 16 foractuating the switch 6. The gain of the amplifier 10 is adjusted bymeans of a rotatable or slidable knob 17. A plurality of slots 18 in thehousing 12 provide an outlet for the produced sound.

What is claimed is:

1. An apparatus for providing an audible indication of the strength ofelectric signals produced in the human body by heart activitycomprising, means for generating an audiofrequency carrier wave, meansfor modulating the frequency thereof in accordance with the strength ofthe electric signals, and means for amplitude modulating the frequencymodulated carrier wave so as to vary the tone strength of the carrierwave in accordance with the strength of the electric signals applied tothe apparatus.

2. A device for the audible observation of heart activity comprising, atleast two electrodes adapted to derive electric signals from the bodyproduced by the action of the heart, means for generating an audiofrequency carrier wave, amplifier means having an input coupled to saidelectrodes, means for coupling the output of said amplifier means to aninput of said audio frequency generating means whereby the carrier waveis frequency modulated in accordance with said electric signals, meanscoupled to the output of said amplifier means and to the output of saidaudio frequency generating means for amplitude modulating the frequencymodulated carrier wave in accordance with said electric signals derivedfrom the human body, and means responsive to the amplitude and frequencymodulated carrier wave for producing an audible indication thereof.

3. A device as claimed in claim 2 further comprising rectifier meansconnected between the output of said amplifier means and an input ofsaid amplitude modulating means.

4. A device as claimed in claim 2 further comprising means forsuppressing the audio frequency carrier wave whenever the electricsignals are below a given threshold level.

1. An apparatus for providing an audible indication of the strength ofelectric signals produced in the human body by heart activitycomprising, means for generating an audiofrequency carrier wave, meansfor modulating the frequency thereof in accordance with the strength ofthe electric signals, and means for amplitude modulating thefrequency-modulated carrier wave so as to vary the tone strength of thecarrier wave in accordance with the strength of the electric signalsapplied to the apparatus.
 2. A device for the audible observation ofheart activity comprising, at least two electrodes adapted to deriveelectric signals from the body produced by the action of the heart,means for generating an audio frequency carrier wave, amplifier meanshaving an input coupled to said electrodes, means for coupling theoutput of said amplifier means to an input of said audio frequencygenerating means whereby the carrier wave is frequency modulated inaccordance with said electric signals, means coupled to the output ofsaid amplifier means and to the output of said audio frequencygenerating means for amplitude modulating the frequency modulatedcarrier wave in accordance with said electric signals derived from thehuman body, and means responsive to the amplitude and frequencymodulated carrier wave for producing an audible indication thereof.
 3. Adevice as claimed in claim 2 further comprising rectifier meansconnected between the output of said amplifier means and an input ofsaid amplitude modulating means.
 4. A device as claimed in claim 2further comprising means for suppressing the audio frequency carrierwave whenever the electric signals are below a given threshold level.